The two are completely separate and do not compete nor were they designed to compete with each other (IMHO they're more complimentary than competitive).
They are not complimentary, because LTC doesn't add anything substantial over BTC. If one of them has the network effects and trust, the other one is useless.
I'm surprised that people ITT have thus far neglected to mention that Litecoin can offer an additional layer of obfuscation for other cryptocurrencies, including Bitcoin.
A BTC mixing service can achieve the same thing with less risk.
I don't see anyone dumping their litecoins even after its price went from 2$ to 40$. Obviously there is a lot of speculation around it but certainly not a pump and dump scheme.
Charles Lee is smart enough to realize that most of the PR he does for Litecoin makes no logical sense, so it seems pretty clear that his primary motivation for advocating Litecoin is financial. I think he knows that eventually it will all come crashing down, but he wants to ride it as far as he can. He's probably been slowly cashing out.